JP3649643B2 - Lithium-ion battery capacity estimation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a lithium ion battery, and more particularly to a method for estimating the capacity of a lithium ion battery.To the lawIt is related.
[0002]
[Prior art]
In recent years, the demand for batteries has increased due to the downsizing, high performance, and portability of various electronic devices. Accordingly, the improvement and development of batteries are becoming increasingly active. New application areas for batteries are also expanding.
[0003]
With the spread of batteries, there is an increasing demand for improving the reliability of these batteries. In particular, nickel-metal hydride batteries (hereinafter referred to as Ni / MH batteries) and lithium ion batteries (hereinafter referred to as Ni / MH batteries), which have a significantly higher energy density than conventional lead batteries and nickel cadmium batteries (hereinafter referred to as Ni / Cd batteries). In Li-ion batteries), the degree of damage caused by an accident can become more serious, so ensuring reliability is an important issue.
[0004]
As one of the reliability, grasping an accurate deterioration state of the on-board battery and timely battery replacement can be mentioned. For high energy density batteries such as Ni / MH batteries and Li-ion batteries, the smart battery system (SBS) proposed by Intel and Duracell in 1994 is a battery management system that includes charge control and remaining capacity determination. It has become popular with improvements (see www.sbs-forum. Or).
[0005]
[Problems to be solved by the invention]
However, for battery degradation, these battery controls / managements are based on a huge amount of information data management that constantly monitors battery current, voltage, temperature, etc., as well as information on manufacturers, battery types, etc. The price of the product has soared in an extremely expensive method.
[0006]
In addition, SBS is control and management of battery charge control, remaining capacity, etc., and does not have a function of grasping the deterioration state of the battery, and replacement of the battery or battery pack depends on the intuition of the user. Was the current situation.
[0007]
Aside from SBS, a control / management system for Li-ion batteries (InfoLithium) mounted on Sony video cameras has been proposed, but, like SBS, it did not have a deterioration determination function.
[0008]
Therefore, if a method for simply estimating the capacity of a Li-ion battery is established, whether or not the battery has deteriorated depends on whether the capacity estimated by the method is larger or smaller than a preset limit capacity. The effect of the method is extremely large.
[0009]
  The present invention has been made in view of the above points, and an object of the present invention is to provide a method for simply estimating the capacity of a Li ion battery, which is essential for determining deterioration of the Li ion battery.Andis there.
[0010]
[Means for Solving the Problems]
  In order to solve the above problems, in the present invention, as described in claim 1,
  It is a method for estimating the capacity of a lithium ion battery.RWhen charging the lithium ion battery by the constant current constant voltage method, from the time when the charging condition is switched from constant current to constant voltageThe charging current value It at the time when 30 seconds or more and the time t within 30 minutes have elapsed is obtained, and the estimated capacity Ct of the lithium ion battery is calculated using the charging current value It as a relational expression,
    Ct / C ₀ = −a × It + b                              (1)
(Here, C ₀ Is a nominal capacity of the lithium ion battery, and a and b are positive value constants determined by the lithium ion battery and the time t). A charging period by a constant current constant voltage method in which a total charging time is 3 hours or more and within one month using a lithium ion battery or the same type of lithium ion battery as From the time when the charge condition is switched from a constant current to a constant voltage in each cycle by repeating a charge / discharge cycle having a pause period provided between the charge period and the discharge period as required five or more times. The elapsed time t at a plurality of time points such that the elapsed time is within a range of 30 seconds or longer and within 30 minutes _ni (Where n is a number given to each cycle, i is a number given to each time point in each cycle) and the charging current value It _ni , And the discharge capacity C obtained by integrating the discharge current with respect to time for each cycle. _n And the recorded elapsed time t _ni And the charging current value It _ni And the discharge capacity C _n From the above, the values of a and b in the relational expression (1) are determined.The capacity | capacitance estimation method of the lithium ion battery characterized by the above is comprised.
[0011]
  In the present invention, as described in claim 2,
  It is a method for estimating the capacity of a lithium ion battery.RWhen charging the lithium ion battery by the constant current constant voltage method, the charging current value It at the time when the time t within 30 minutes has elapsed for 30 seconds or more from when the charging condition is switched from constant current to constant voltage is obtained. And using the charging current value It, the estimated capacity Ct of the lithium ion battery is expressed by a relational expression:
    Ct / C₀= −a × It + b (1)
(Here, C₀Is a nominal capacity of the lithium ion battery, and a and b are positive constants determined by the lithium ion battery and the time t).A capacity estimation method for a lithium ion battery, wherein the values of a and b in the relational expression (1) are expressed as a function of the time t,
    a = d × t ^e                                             (2)
    b = f × t ^h                                             (3)
(Where d, e, f, h are constants determined by the lithium ion battery, and 0 <d, e <0, 0 <f, h <0). A constant current and constant voltage method using a lithium ion battery whose capacity is to be estimated or a lithium ion battery of the same type as the lithium ion battery, wherein the total charge time for one time is 3 hours or more and 1 month or less A charge / discharge cycle having a charging period, a discharging period, and a pause period provided between the charging period and the discharging period as necessary is repeated five times or more, and the charging condition is set to a constant current in each cycle. The elapsed time t at a plurality of time points such that the elapsed time from the time when the voltage is switched to the constant voltage is within a range of 30 seconds or more and 30 minutes or less. _ni (Where n is a number given to each cycle, i is a number given to each time point in each cycle) and the charging current value It _ni , And the discharge capacity C obtained by integrating the discharge current with respect to time for each cycle. _n And the recorded elapsed time t _ni And the charging current value It _ni And the discharge capacity C _n From these, the values of d, e, f, and h in the above relational expressions (2) and (3) are determined.The capacity | capacitance estimation method of the lithium ion battery characterized by the above is comprised.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The Li-ion battery capacity estimation method according to the present invention will be described in more detail with reference to the drawings. In the following description, a “battery pack” refers to a single battery or a plurality of single batteries connected in series, parallel, or a combination of both, integrated with a safety control circuit or charge / discharge control circuit. It means “secondary battery as an independent power source”.
[0018]
FIG. 1 is a diagram showing changes over time in battery voltage and current value during charging of a Li-ion battery. In FIG. 1, the battery or the Li ion battery in the battery pack (hereinafter collectively referred to as a Li ion battery) is first set in a constant current (CC) mode to an upper limit set in advance at a predetermined constant current value. After charging to voltage V1 (usually 4.1V / cell or 4.2V / cell, where “cell” means a single cell), after the voltage of the Li-ion battery reaches the set voltage V1 Then, charging in the constant voltage (CV) mode is started.
[0019]
When charging by such a constant current / constant voltage method, the current value It when a predetermined time t has elapsed since the charging condition was switched from the constant current mode to the constant voltage mode is calculated. If the capacity is constant, the current value It is also constant. However, when the time t is within a certain range, the current value It increases as the battery capacity decreases.
[0020]
The inventors of the present invention have found a remarkable correlation between the above-described decrease in capacity and increase in current, and have made the present invention.
[0021]
  Embodiments of the present invention will be specifically described below.
  In the present inventionWhen charging a lithium-ion battery subject to capacity capacity estimation using the constant current / constant voltage method, the charging current value at the time when a preset time has elapsed from when the charging condition was switched from constant current to constant voltage The capacity of the lithium ion battery is estimated using the charging current value.
[0022]
  In order to enable such estimation, a lithium ion battery having the same structure and the same specification as the target of capacity estimation (referred to as the same type in this specification), the capacity thereof Prepare a plurality of different ones (depending on the cause of repeated use, etc.), use them to repeat the charge / discharge cycle, measure the charge current value at the above point, and determine the battery capacity and the charge current value from the results. Find the correlation with. The correlation at this time does not necessarily need to be expressed by an analytical mathematical expression, and may be expressed by a broken line connecting the measurement points in the correlation diagram with a straight line.However, in the present invention, only the case where the above correlation is expressed by an analytical mathematical expression is targeted..
[0023]
  furtherWhen a linear relationship (linear function relationship) is adopted as the correlation, there is a preferable range for the above time. As shown in specific example 2 described later (particularly FIG. 5), a preferable range of the above time that causes only a small error is 30 seconds or more and 30 minutes or less, and a more preferable range is 30 seconds or more and 20 minutes or less. is there.
[0024]
  In this embodiment,above“Preset time” is t, and the time t is 30 seconds or more and 30 minutes or less. Under such restrictions, the relational expression (1), that is, the estimated capacity Ct of the battery and the charging current value It,
    Ct / C₀= −a × It + b (1)
(Here, C₀Is a nominal capacity of the lithium ion battery, and a and b are positive constants determined by the lithium ion battery and the time t), which is practically convenient. As shown in specific example 2 (particularly FIG. 5) to be described later, a preferable range of the time t that causes only a small error is 30 seconds or more and 30 minutes or less, and a more preferable range is 30 seconds or more and 20 minutes or less. It is.
[0025]
In addition, at a time point of less than 30 seconds after the start of CV mode charging, there is a case where the variation in the charging current value becomes large, and it is not always possible to accurately estimate the capacity. In addition, when the time exceeds 30 minutes after the start, the relationship between the charging current value and the capacity changes, and the relational expression becomes complicated by deviating from a simple linear relationship.
[0026]
Monitoring for obtaining the current value It is performed several times every 10 μs, for example, and a method of selecting an intermediate value or selecting an average value is preferable as a method of suppressing erroneous recognition due to noise. However, the monitoring method is not limited as long as the capacity estimation method according to the present invention can be implemented.
[0027]
  The estimated capacity Ct of the battery is calculated by the relational expression (1) using the current value It. At this time, it is necessary to know the values of a and b in the relational expression (1).See belowThere is a way.
[0028]
  When determining the deterioration of the battery from the estimated capacity Ct, the nominal capacity C₀Relational expression for
  Deg (%) = 100 × (1-Ct / C₀(4)
The deterioration degree Deg (%) is calculated by the above, and when the deterioration degree Deg (%) becomes larger than a predetermined limit value, it can be determined that the battery has deteriorated..
[0029]
  Also, The values of a and b in the relational expression (1) are the relational expressions (2) and (3), that is,
    a = d × t^e                                            (2)
    b = f × t^h                                            (3)
(Where d, e, f, and h are constants determined by the lithium ion battery, and 0 <d, e <0, 0 <f, h <0).May.
[0030]
  At this time, it is necessary to know the values of d, e, f, and h in the above relational expressions (2) and (3).See belowThere is a way.
[0031]
For many cases, the values of d, e, f, and h were obtained. When the unit of It is A and the unit of t is minutes, these values are:
1.4 ≦ d ≦ 2.2
−0.7 ≦ e ≦ −0.3
1.4 ≦ f ≦ 2.2
−0.25 ≦ h ≦ −0.15
Was found to satisfy.
[0032]
In addition, in the relational expression (1), it is claimed that the charging current value It satisfies a condition that monotonously decreases as the time t increases in the same battery having an arbitrary estimated capacity value Ct.
[0033]
The reason why the coefficients a and b in the relational expression (1) are a function of the measurement time t is that, when charging in the constant current (CV) mode, the current value depends on the diffusion of Li into the active material. It has been known. If the in-solid diffusion of Li into the active material is according to Fick's first law, the current value I is related to the time t from the start of the CV mode.
I = KnF [(Δc) / t^1/2]
(Where K is a constant, Δc is a value corresponding to the concentration gradient of Li in the solid, n is an electrochemical equivalent, and F is a Faraday constant).
[0034]
However, since there are various factors in reality, it can be a more complicated function of t. The constants a and b of the deterioration judgment formula (1) in the present invention can be obtained by measuring the current value It at an arbitrary time t with 0.5 ≦ t ≦ 30. Therefore, it is a high-order function of the measurement time t.
[0035]
With values other than the constant conditions shown above, the current value It takes a negative value in a very short time within one minute, or the charging current value It has a maximum value at a certain time t. In practice, it is not always possible to specifically express the change in the charging current of the Li-ion battery by a formula.
[0036]
  Note that the estimated capacity Ct shown in the relational expression (1) is a capacity at the time of complete discharge discharged from a fully charged state to a predetermined lower limit voltage, and does not indicate a discharge capacity up to an arbitrary voltage in the middle. Absent.
  BookIn the embodiment,By the following method,The values of a and b in the above relational expression (1) or the values of d, e, f and h in the above relational expressions (2) and (3) are determined, and the determined values are used.Estimating lithium-ion battery capacity. That is,
  Using the same type of lithium ion battery as the target of capacity estimation or the lithium ion battery,
  A charging period according to a constant current constant voltage method in which a total charging time for one time is 3 hours or more and within one month, a discharging period, and a pause period provided between the charging period and the discharging period as necessary And repeating the charge / discharge cycle having 5 or more times,
  In each cycle, the elapsed time t at a plurality of time points such that the elapsed time from when the charging condition is switched from constant current to constant voltage is within a range of 30 seconds or more and 30 minutes or less._ni(Where n is a number given to each cycle, i is a number given to each time point in each cycle) and the charging current value It_ni, And the discharge capacity C obtained by integrating the discharge current with respect to time for each cycle._nAnd the recorded elapsed time t_niAnd the charging current value It_niAnd the discharge capacity C_nFrom the above, the values of a and b in the relational expression (1) or the values of d, e, f and h in the relational expressions (2) and (3) are determined, and the determined values are used.Estimating lithium-ion battery capacity.
[0037]
For the determination of the above numerical values, a successive approximation method, a least square method, or the like may be used.
[0038]
Specific charging / discharging cycles include the following. That is,
Using the Li ion battery or the same type of Li ion battery that is the target of capacity estimation,
A constant current and a constant voltage under a charge upper limit voltage setting that is recommended as a charge condition or a condition in which a battery is installed or a charger to be used, which is a charge current value that results in a charge rate of 0.5C or more and 2C or less (CC-CV) method, a charging period with a charging time of 3 hours to 1 month,
A discharge current value that results in a discharge rate of 0.2C or more and 2C or less, or a discharge period that is recommended as a discharge condition, or under a discharge end voltage condition setting specified by a battery-mounted device or a charger to be used ,
A charge / discharge cycle having a pause period provided between the charge period and the discharge period as necessary is defined as a charge / discharge cycle for capacity estimation.
[0039]
When the charging current value exceeds 2C, it exceeds the normal operating current, damages the battery, and an accurate deterioration judgment formula cannot be constructed. In addition, a low charge rate of less than 0.5 C is not preferable because it takes too much time to construct a deterioration determination formula.
[0040]
If the charging time of each cycle is less than 3 hours, there is a possibility that charging may be insufficient when the Li-ion battery is deteriorated, which will provide a deterioration determination formula that is difficult to accurately determine deterioration. Absent.
[0041]
In addition, if the charging time exceeds one month, it takes an enormous amount of time to construct the deterioration judgment formula, which is not preferable.
[0042]
Moreover, in order to obtain | require this degradation determination formula, in order to determine the coefficient, the charging / discharging cycle used as the said conditions is implemented at least 5 cycles or more. Since the deterioration judgment formula (1) according to the present invention is a linear function, it is possible to determine the coefficient using data of at least two cycles. However, in actuality, if the data is four cycles or less due to an error in reading the current value, etc. The error exceeds ± 20%, which is not preferable. In order to ensure a determination accuracy within ± 20%, it is preferable to acquire data for at least 5 cycles. Furthermore, the measurement of the current value It in each cycle of three or more cycles that is the target of data acquisition is performed at two different points of time that have elapsed since the change to the CV mode, and the respective coefficients d describing the constants a and b. , E, f, and h are difficult to determine.
[0043]
  In the Li-ion battery capacity estimation method according to the present invention, the relational expression (1) is preferably obtained at 10 ° C. or higher and 45 ° C. or lower. Under a low temperature of less than 10 ° C., a linear relationship is not established between the capacity Ct and the charging current value It as in the relational expression (1). Moreover, at a temperature higher than 45 ° C., it does not become compatible with the operating temperature range of the Li ion battery. Further, the capacity estimation is performed at an environmental temperature within a range of ± 10 ° C. and within a range of 10 ° C. or higher and 45 ° C. or lower with respect to the environmental temperature when the relational expression (1) is obtained. It is desirable. When the environmental temperature is higher than + 10 ° C. and lower than −10 ° C. from the temperature at which the relational expression is obtained, the value of the charging current value is different, making it difficult to accurately estimate the capacity.
[0044]
(Reference Example 1)
  BookReference exampleIn
  Use of a lithium ion battery pack having a safety ensuring means with a built-in IC, and calculate the estimated capacity value of the lithium ion battery in the lithium ion battery pack to the IC or an IC attached to the IC and expanded. An empty memory for storing a numerical value to be used; and an arithmetic circuit for calculating the estimated capacity value from the numerical value and a charging current value during charging of the lithium ion battery when the numerical value is stored in the empty memory; A lithium ion battery pack is provided.
[0045]
In such a lithium ion battery pack, when the lithium ion battery in the pack is charged, the estimated capacity value of the battery is calculated, and the value is obtained via the connection terminal of the IC to the outside. The battery pack may be provided with a means for outputting a warning indicating capacity deterioration when the estimated capacity value is smaller than a preset limit capacity value. . As this warning, a warning by displaying characters or images, a warning by signal sound, a warning by voice, or the like is used.
[0046]
  Further, as a method of calculating the estimated capacity value of the lithium ion battery from the charging current value during charging of the lithium ion battery and other numerical values, for example, claim 1Or 2The method for estimating the capacity of a lithium ion battery described in 1) can be used.
[0047]
As is clear from the above description of the embodiment, the Li-ion battery capacity estimation method according to the present invention is an extremely simple method, and it is possible to easily and easily reduce the capacity deterioration of the Li-ion battery. Judgment can be made and a remarkable practical effect appears.
[0048]
  Also,Described in Reference Example 1 aboveIn the Li-ion battery pack, the capacity of the battery in the battery pack can be estimated simply by using the battery pack, thereby automatically determining the capacity deterioration of the battery. Therefore, the practical effect is extremely large.
(Specific examples of implementation)
  Next, an example of a method for concretely implementing the method for estimating the capacity of a Li ion battery according to the present invention will be outlined.
[0049]
FIG. 2 shows a concept of a charge control circuit for performing the above method. In the figure, 1 is a charge control circuit, 2 is a Li-ion battery to be determined, 3 is a microcomputer for charge control, 4 is Power supply microcomputer, 5 is a switch, 6 is a thermistor, 7 is an abnormal output detection terminal, 8 is a battery connection positive terminal, 9 is a battery connection negative terminal, 10 is a power supply connection positive terminal, and 11 is a power supply connection negative terminal.
[0050]
In order to realize the capacity estimation method of the present invention, time measurement by a timer and measurement of the charging current value It are necessary. However, the timer is originally mounted on the charging control microcomputer 3 and the current value It abnormal output detection is performed. It is possible to monitor using the terminal 7 or the like, and the arithmetic processing of the above relational expression (1), (2) or (3) may be performed using an empty memory such as the microcomputer 3 for charge control. It is possible to perform capacity estimation according to the present invention without the need for additional components. However, there is no limitation to this as long as the capacity estimation can be performed.
[0051]
As described above, the capacity estimation method for a Li-ion battery according to the present invention can be implemented with a function added to the main body of the mounted device. It can be provided in a safety mechanism in the pack. This will be described below using a specific safety circuit diagram.
[0052]
FIG. 3 is a diagram showing a general circuit configuration of a Li-ion battery pack, in which three Li-ion batteries are mounted in series.
[0053]
In FIG. 3, 12 is a battery pack body, and 13-1, 13-2, and 13-3 are Li ion batteries. A protection IC 14 monitors voltage, current, temperature, etc. and performs software safety control. 15-A, 15-B, 15-C, 15-1, 15-2, 15-3 are FETs for controlling charging current in the pack and each battery, and 16 is a PTC element that is a thermal fuse , 17 are current fuses, each of which plays a role of cutting off the current when the temperature rises and when the current is abnormally large. 18 is a plus terminal, 19 is a minus terminal, and 20 is a terminal for outputting and controlling information.
[0054]
In FIG. 3, a timer is mounted in the protection IC 14 of the safety mechanism, and the relational expression (1) between the charge current value It and the discharge capacity Ct shown above is input in advance to a free memory, and a constant current ( The charge current value It at 15-A, 15-B, or each battery at a predetermined elapsed time t within a range of 30 seconds or more and 30 minutes or more after the charge mode is changed from CC) to constant voltage (CV) Are monitored by FETs 15-1, 15-2, and 15-3, and the calculated charging current value It is substituted for calculation. If necessary, an additional IC can be provided at an appropriate position in the pack separately from the protection IC 14. The calculated result is output to the apparatus main body for display and emission on an appropriate display or warning sound through the terminal 20.
[0055]
As described above, a Li-ion battery pack having a capacity estimation function, for example, a capacity estimation function according to the present invention, can be provided by a minimum change of the existing Li-ion battery pack. However, the present invention is not limited to the above configuration as long as the capacity of the Li ion battery can be estimated.
[0056]
As a method for estimating the capacity of a Li-ion battery according to the present invention and the application of a Li-ion battery pack having the capacity estimation function, a device that particularly requires high reliability is conceivable. By grasping the deterioration state of the battery and realizing timely battery replacement, troubles in the device can be avoided.
[0057]
However, as long as the device is equipped with a Li-ion battery, there is no problem in adopting the Li-ion battery having the capacity estimation method and the capacity estimation function, and it is possible to realize battery replacement without waste. As a result, the practical advantages are extremely large.
[0058]
Although the capacity | capacitance estimation method of the Li ion battery which concerns on this invention is demonstrated by a more specific example below, this invention is not limited to this at all.
(Specific example 1)
A prismatic Li-ion battery (nominal capacity 600 mAh) is prepared, and using a battery charging / discharging device having a data collection / storage function, a charging current value 600 mA (charging current rate 1 C), a charging upper limit voltage 4.1 V, and a charging time 3 hours Charging / discharging with a constant current constant voltage (CC-CV), discharge current value 600mA (discharge current rate 1C), discharge end voltage 2.75V, and charging / discharging each with 1 hour rest The cycle is repeated 10 times, and the charging current value It (at an arbitrary time t (in minutes) within 30 seconds and 30 minutes after changing from the constant current (CC) to the constant voltage (CV) in each cycle. The unit was A), and the discharge capacity was measured.
[0059]
As a result, the coefficient a is
a = 1.92 × t^-0.5                                    (5)
And the coefficient b is
b = 1.92 × t^-0.2                                    (6)
Relational expression
Ct / C₀= −a × It + b (7)
(Here, C₀Is the nominal capacity of this battery.
[0060]
By the way, when trying to obtain the relational expressions (5) and (6) above using the data for the initial 5 cycles of the charge / discharge cycle, the same value as the constant shown above was obtained, but the data for only the initial 4 cycles. However, the variation was so large that the relational expression could not be obtained.
[0061]
In addition, among the above charge / discharge conditions, a charge / discharge cycle test was performed with only the charge time being 2 hours, but a linear relationship was not obtained between the charge current It and the discharge capacity, and equation (7) was not obtained. It was.
[0062]
Separately, a rectangular Li-ion battery of the same kind (nominal capacity 600 mAh) was used as a test battery, and a battery charging / discharging device having a data collection / storage function was used. Charging current value 600 mA, charging upper limit voltage 4.1 V, charging time 7 days (168 hours ) With a constant current constant voltage (CC-CV), a discharge current value of 600 mA, a discharge with a final discharge voltage of 2.75 V, and a charge / discharge cycle test with a pause of 1 hour between each charge and discharge, Capacity C in each cycle_nThen, the validity of the relational expression (7) was examined by measuring the charging current value It after a predetermined time t after the change to the CV mode.
[0063]
The results are shown in FIG.
[0064]
  Figure 4 shows the discharge capacity of the test battery for each cycle.Amount C _n ofNominal capacity C₀Ratio to (C_n/ C₀In the figure, nominal capacity ratio C_mAnd charging current value It (in the figure, I₅And display). FIG. 4 shows the measured capacity C_nAnd nominal capacity C₀The scale of deterioration obtained from the above is also shown. In the figure, the solid line indicates the relational expression (7).
[0065]
That is, since t = 5, a in (5) is a = 0.86, b in (6) is b = 1.39, and the capacity estimation formula is Ct / C₀C₅Represented by
C₅= -0.86 x I₅+1.39 (8)
It became.
[0066]
In addition, the two broken lines in FIG. 4 indicate the estimated capacity value C calculated by the determination formula (8).₅Actual capacity C_mAs a value for
Err (%) = 100 × (C₅-C_m(9)
Estimated capacity C corresponding to ± 5%₅The value of is shown.
[0067]
As is apparent from the results of FIG. 4, according to the capacity estimation method according to the present invention, it is possible to determine the deterioration state of the Li ion battery with very good accuracy within an error of ± 5%.
(Specific example 2)
A rectangular Li-ion battery (nominal capacity 600 mAh) mounted on the same type of mobile phone as used in Example 1 is collected, and a charging current value of 600 mA is obtained using a battery charging / discharging device having a data collection / storage function. (Charging current rate 1C), charging upper limit voltage 4.1V, charging with constant current constant voltage (CC-CV) for 3 hours charging time, rest for 1 hour, discharge current value 600mA (discharge current rate 1C), discharge end voltage Two cycles of charging and discharging were performed with a discharge of 2.75 V and a one hour rest as one cycle. The charging current value It at each time t, which is 35 minutes after the mode is changed from the constant current (CC) to the constant voltage (CV), and the discharge capacity at the second cycle are expressed as the nominal capacity C.₀The value divided by C is C_mAnd using the judgment formula (7) in the present invention obtained in the specific example 1, the estimated capacity Ct is changed to the nominal capacity C₀Value divided by (Ct / C₀, This is C_tThe accuracy of the determination was examined in comparison with Judgment accuracy is estimated value C_tMeasured value C_mAs above, the deviation from
Err (%) = 100 × (C_t-C_m(9 ’)
Thus, the magnitude of the error was evaluated.
[0068]
The results are shown in FIG.
[0069]
FIG. 5 shows the charging current value It at each time t until 35 minutes after the start of CV charging, the average value of the error calculated by the above equation (9 ′), the absolute value of the maximum error, and the absolute value of the minimum error. FIG.
[0070]
As is apparent from FIG. 5, the error from 0.5 minutes to 30 minutes after the start of CV charging is within ± 20%, which is not a problem in actual use, and further, 20 minutes after 0.5 minutes. The error until later is within ± 6%, which indicates that the capacity estimation method of the present invention provides excellent determination accuracy.
[0071]
It was found that when the time is shorter than 0.5 minutes after the start of CV charging, the determination accuracy is out of the range of ± 20%, and the error becomes large, causing a problem in actual use. For example, in the result based on the capacity estimation equation (7) 0.33 minutes (20 seconds) after the start of CV charging and the equation (9 ′) for obtaining an error, the maximum error (absolute value) 29%, the minimum error ( (Absolute value) 0.19%, average error + 26%. Therefore, it became clear that measurement in less than 0.5 minutes after the start of CV charging is not preferable as far as this calculation method is concerned.
[0072]
Further, it has been found that if it exceeds 30 minutes after the start of CV charging, the determination accuracy falls outside the range within ± 20%, and the error becomes large, causing a problem in actual use.
[0073]
As a reason for this, it has been recognized that a linear relationship between the capacity and the charging current value does not hold at an elapsed time longer than 30 minutes after the start of CV charging. As an example, FIG. 6 shows the result of 31 minutes after the start of CV charging, which was obtained for reference in the charge / discharge cycle test performed when obtaining the relational expressions (5), (6), and (7) in Example 1. It was. FIG. 6 shows the charging current value I at 31 minutes after the start of CV charging.₃₁(A) and discharge capacity C_mIn the figure, the solid line indicates the capacity estimation formula (7) at t = 31, and the two broken lines indicate the estimated capacity C when the error is ± 20% obtained from the formula (9 ').₃₁The value of is shown.
[0074]
As shown in FIG. 6, the discharge capacity C exceeds 30 minutes after the start of CV charging._mAnd the charging current value It deviate from the linear relationship, and cannot be represented by a simple capacity estimation formula in the present invention, and require complicated high-order formulas. It was found that there was a risk of rising.
(Specific example 3)
Li-ion battery of the same kind as in Example 1 (nominal capacity 600 mAh), 3 cells, a safety protection function, a protection IC with a timer and the relational expressions (5), (6), (7) in Example 1 above and its A Li-ion battery pack having the configuration shown in FIG. 3 was prepared, which was equipped with an IC in which a calculation function was input in advance.
[0075]
The IC 14 is charged with a charging current value I 10 minutes after changing from a constant current (CC) to a constant voltage (CV).₁₀(A) is set to be monitored, and the charging current value I₁₀The capacity estimation formula in the present invention for
C₁₀= −0.61 × I₁₀+1.21 (10)
It was confirmed that
[0076]
This battery pack is installed in a charging / discharging test apparatus having a data collection and management function, a charging current value of 600 mA (charging current rate of 1 C), a charging upper limit voltage of 4.1 V, and a constant current and constant voltage of 10 days (CC-CV). ), A discharge current value of 600 mA (discharge current rate 1 C), a discharge with a final discharge voltage of 2.75 V, and a charge / discharge cycle with a pause of 1 hour between each charge and discharge are repeated 15 times to obtain a constant current ( CC) charging current value I after 10 minutes from changing to constant voltage (CV)₁₀And the measured capacitance value C of the discharge_nAnd measure C_nNominal capacity C₀Divide by C_mIt was.
[0077]
The results are shown in FIG.
[0078]
That is, FIG. 7 shows the charging current value I in the specific example 3.₁₀And discharge capacity C_mIt is the figure which showed the relationship. In the figure, the solid line represents I in the above-described determination formula (10).₁₀And C₁₀The two broken lines represent I in the case of an error of ± 5% at t = 10 based on the formula (9 ′) shown in the specific example 2.₁₀And C₁₀Is a straight line showing the relationship.
[0079]
As is apparent from FIG. 7, in the Li ion battery pack having the capacity estimation function according to the present invention, the capacity C is within an error range of ± 5%._mThus, it was found that the present invention can provide a Li-ion battery pack capable of realizing highly accurate capacity estimation.
[0080]
【The invention's effect】
  As described above, the present invention provides a method for simply estimating the capacity of a Li ion battery, which is essential for determining the deterioration of the Li ion battery.TogaAnd can make a significant contribution in practice.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the concept of changes in battery voltage and charging current value by a constant current constant voltage (CC-CV) system, which is a general charging method for lithium ion batteries.
FIG. 2 is a conceptual block diagram of a charge control circuit configuration to which the lithium ion battery capacity estimation method according to the present invention is specifically applied.
FIG. 3 is a diagram illustrating a configuration example of a Li ion battery pack having a capacity estimation function according to the present invention.
FIG. 4 is a diagram showing a relationship between a charge current value and a discharge capacity, showing a test result in Example 1 of the present invention.
FIG. 5 is a diagram illustrating a relationship between a measurement time and a determination error indicating a test result in a specific example 2 of the present invention.
FIG. 6 is a diagram showing the relationship between the charge current value and the discharge capacity, showing the test results in Example 2 of the present invention.
FIG. 7 is a diagram showing the relationship between the charge current value and the discharge capacity, showing the test results in Example 3 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Charge control circuit, 2 ... Battery, 3 ... Charge control microcomputer, 4 ... Power supply microcomputer, 5 ... Switch, 6 ... Thermistor, 7 ... Abnormal output detection terminal, 8 ... Battery connection positive terminal, 9 ... Battery connection minus terminal DESCRIPTION OF SYMBOLS 10 ... Power supply positive terminal, 11 ... Power supply negative terminal, 12 ... Battery pack main body, 13-1, 13-2, 13-3 ... Li ion battery, 14 ... Protection IC, 15-A, 15-B , 15-C, 15-1, 15-2, 15-3... FET, 16... PTC element, 17... Current fuse, 18.

Claims (2)

Ri methods der to estimate the capacity of the lithium ion battery, the lithium-ion battery when charged by the constant current and constant voltage method, more than 30 seconds from the time of switching the charging condition from constant current to constant voltage, within 30 minutes A charging current value It at the time when time t has elapsed is obtained, and the estimated capacity Ct of the lithium ion battery is calculated using the charging current value It as a relational expression:
Ct / C ₀ = −a × It + b (1)
(Here, C ₀ is the nominal capacity of the lithium ion battery, a, b is a is a positive value constants determined by the said lithium ion battery and said time t) was a volume estimation method of the lithium ion battery be calculated by And
Using the same type of lithium ion battery as the target of capacity estimation or the lithium ion battery,
A charging period according to a constant current constant voltage method in which a total charging time for one time is 3 hours or more and within one month, a discharging period, and a pause period provided between the charging period and the discharging period as necessary And repeating the charge / discharge cycle having 5 or more times,
In each cycle, the elapsed time t _ni at a plurality of time points where the elapsed time from the time when the charging condition is switched from constant current to constant voltage is in the range of 30 seconds or more and 30 minutes or less (where n is each A number given to each cycle, i being a number given to each time point in each cycle) and the charging current value It _ni , and a discharge capacity C obtained by integrating the discharge current with respect to time for each cycle. lithium recording the _n, and from the recorded the elapsed time t _ni and the charging current value it _ni and the discharge capacity C _n, wherein the determining a, the value of b in the above equation (1) Ion battery capacity estimation method. It is a method for estimating the capacity of a lithium ion battery, and when charging the lithium ion battery by a constant current constant voltage method, it takes 30 seconds or more and 30 minutes or less from when the charging condition is switched from constant current to constant voltage. The charging current value It at the time when t has elapsed is obtained, and the estimated capacity Ct of the lithium ion battery using the charging current value It is expressed by a relational expression:
Ct / C ₀ = −a × It + b (1)
(Where C ₀ is the nominal capacity of the lithium ion battery, and a and b are positive constants determined by the lithium ion battery and the time t). ,
Using the values of a and b in the relational expression (1) as a function of the time t,
^{a = d × t e (2} )
b = f × t ^h (3)
(Here, d, e, f, h is a constant determined by the lithium ion battery, 0 <d, e <0,0 <f, h < 0) volume estimate of the lithium ion battery you calculated by A method,
Using the same type of lithium ion battery as the target of capacity estimation or the lithium ion battery,
A charging period according to a constant current constant voltage method in which a total charging time for one time is 3 hours or more and within one month, a discharging period, and a pause period provided between the charging period and the discharging period as necessary And repeating the charge / discharge cycle having 5 or more times,
In each cycle, the elapsed time t _ni at a plurality of time points where the elapsed time from the time when the charging condition is switched from the constant current to the constant voltage is within a range of 30 seconds or more and 30 minutes or less (where n is each Cycle number, i is a number assigned to each time point in each cycle) and the charging current value It _ni , and the discharge capacity C obtained by integrating the discharge current with respect to time for each cycle. recording the _n, and a recorded the elapsed time _{t ni} and the charging current value _{It ni} and the discharge capacity _{C n,} the relational expression (2), d, e, f, the value of h in (3) features and to Brighter lithium ion capacity estimation method of a battery to be established.

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